Why does a cook use stainless steel pans? Firstly, because they are hygienic and do not emit taste into the food, and secondly, they are easier to clean. The same applies to wine making — grapes retain their aroma and taste best in stainless steel. These tanks indispensable for the production of white wine — they are easier to cool and this cooling leads to fresh types of wine with subtle flavors.
Wooden barrels are another story. Especially in oak tannins are present and they give the wines additional flavors, such as vanilla or tobacco aromas. Such aromas are especially popular among red wines — that is why reds are often aged in oak barrels. Good winemakers usually age only their best wines in barrels or age them in different tanks, barrels (new or old) until the wine reaches the desired balanced aroma and taste.